docs: def check_dataset(dataset, mode):
    """Validate we have a good dataset."""
  
    names = [x['name'] for x in dataset.schema]
    types = [x['type'] for x in dataset.schema]
    if mode == 'train':
      if (set(['image_url', 'label']) != set(names) or any(t != 'STRING' for t in types)):
        raise ValueError('Invalid dataset. Expect only "image_url,label" STRING columns.')
    else:
      if (set(['image_url']) != set(names) and set(['image_url', 'label']) != set(names)) or \
              any(t != 'STRING' for t in types):
        raise ValueError('Invalid dataset. Expect only "image_url" or "image_url,label" ' +
                         'STRING columns.')